This invention relates to an image coding method, image coding apparatus and data storage medium and, more particularly, to an image coding method and image coding apparatus which perform coding of an image signal having no shape value in combination with coding of a shape value independent of a pixel value, and generate a multiplex coded signal including shape value information and pixel value information, and a data storage medium which contains a program for implementing the coding process according to the image coding method by software.
In recent years, we have greeted the age of multimedia in which audio, video and other data are integrally handled, and the conventional information media (i.e., means for transmitting information to men), such as newspapers, magazines, televisions, radios, and telephones, have been adopted as the subjects of multimedia. Generally, xe2x80x9cmultimediaxe2x80x9d means to represent, not only characters, but also diagrams, speeches, and especially images in relation with each other. In order to handle the conventional information media as the subjects of multimedia, it is necessary to transform the information into a digital format.
When the quantity of data possessed by each information medium described above is estimated as the quantity of digital data, in the case of characters, the data quantity for each character is 1xcx9c2 bytes. However, in the case of speech, the data quantity is 64 kbits per second (quality for telecommunication) and, in the case of moving picture, it is more than 100 Mbits per second (quality for current television broadcasting). So, as for most of the information media described above, it is not practical to handle such massive data as it is in the digital format. For example, although visual telephones have already been put to practical use by ISDN (Integrated Services Digital Network) having a transmission rate of 64 kbpsxcx9c1.5 Mbps, it is impossible to transmit an image of a television camera as it is by the ISDN.
So, data compression technologies are demanded. In the case of visual telephones, the moving picture compression technologies standardized as H.261 and H.263 by ITU-T (International Telecommunication Union-Telecommunication Sector) are employed. Further, according to the data compression technology based on MPEG1, it is possible to record image data, together with audio data, in an ordinary music CD (compact disk).
MPEG (Moving Picture Experts Group) is an international standard of data compression for data of a moving picture (an image signal of a moving picture). In MPEG1, data of a moving picture is compressed to 1.5 Mbps, i.e., data of a television signal is compressed to about 1/100. Since the transmission rate to which MPEG1 is directed is limited to mainly about 1.5 Mbps, MPEG2 is standardized to meet the demand for higher image quality. In MPEG2, data of a moving picture is compressed to 2xcx9c15 Mbps.
Under the existing circumstances, standardization of MPEG4 is now proceeded by the working group for standardization of MPEG1 and MPEG2 (ISO/IEC JTC1/SC29/WG11). MPEG4 enables coding and signal processing. in object units, and thereby realizes new functions required in the age of multimedia.
MPEG4 is characterized in that the coding of image signals is performed in object units. In MPEG4, the image signals are not coded in units of frame as an image space having a rectangular shape as in MPEG1 and MPEG2, but the coding of the image signals is performed in object units. To be specific, a shape value which indicates the shape of an object and a pixel value which indicates the design of the object are coded as the image signal.
When the shape value of the object is coded in this way, the new function that the users can freely compose images corresponding to coded image signals and display the images can be realized, as in image composition process in the computer graphics. For the pixel value of a pixel located outside of the object. (outside-object pixel value) which does not require the coding, the coding process can be omitted and thereby the compression rate for the image signal can be improved.
FIG. 24 is a schematic diagram for explaining an image signal including shape information.
The image signal including the shape information includes two signal values, i.e., a pixel value which represents the design of an object to be displayed and a shape value which represents the shape of the object to be displayed. For example, as shown in FIG. 24, an image signal including shape information of a moving picture includes pixel values which form each of pixel VOPs (Fv1xcx9cFv5) and shape values which form each of shape VOPs (Fs1xcx9cFs5). Here, the pixel VOPs (Fv1xcx9cFv5) and their corresponding shape VOPs (Fs1xcx9cFs5) are displayed at display times t1xcx9ct5, respectively, as shown in FIG. 24.
When a natural image is taken by a camera, an image signal obtained by picture-taking by the camera as the camera output includes only a pixel value out of the two signal values (shape value and pixel value). Thus, in the prior art image coding process, the process for generating a shape value indicating the shape of a specific area (object) in the natural image is performed on the basis of the pixel value included in the image signal, with using the image processing technology for subjecting the frame of the natural image to a processing such as area separation, area segmentation and area extraction.
FIG. 25 is a block diagram illustrating a structure of a prior art image coding apparatus which performs the image coding process, using the shape value according to MEG4.
In MEPG4, the concept equivalent to a frame which constitutes video-of natural images or the like, i.e., the frame which constitutes video of a specific area (object) and which is updated with the passage of time is defined as VOP (video object plane). Further, the coding in MPEG4 is performed in block units and macroblock units as in MPEG1 and MPEG2. Here, the macroblocks are image areas which are obtained by dividing the VOP. Each of the image areas is composed of 16 pixelsxc3x9716 pixels. The blocks are image areas which constitute the macroblock. Each of the image areas is composed of 8 pixelsxc3x97pixels.
This image coding apparatus 200 has an IP decision unit 1 for deciding whether a target VOP for which various parameters are set and which is to be coded on the basis of these parameters is assumed to be a VOP subjected to intra-frame coding (I-VOP) or a VOP subjected to inter-frame coding (P-VOP), and outputting a coding mode signal IPmode indicating which type of the coding is to be performed to the target VOP, and a shape extractor 2 for extracting a shape value Spel indicating the shape of the specific area on the basis of the pixel value Vpel associated with the specific area.
This image coding apparatus 200 further has a transparency judgement unit 3 for judging whether the target block in the target VOP to be subjected to the coding requires the coding or not on the basis of the shape value Spel, and outputting the result of the judgement as block transparency information Dtran of the target block, a shape encoder 4 for coding the shape value Sple on the basis of the block transparency information Dtran and the coding mode signal IPmode, and a pixel encoder 5 for coding the pixel value Vpel on the basis of the block transparency information Dtran, the coding mode signal IPmode, and the shape value Spel.
The transparency judgement unit 3 judges whether the pixels in the target block are all outside-shape pixels located outside of the specific area and the target block does not require coding, or at least part of the pixels in the target block are inside-shape pixels located inside of the specific area and the target block requires coding, and outputs the block transparency information Dtran corresponding to the result of the judgement. The shape encoder 4 has a structure which outputs a code for indicating that the target block is an outside-object block when the block transparency information Dtran indicates this, and outputs a shape coded data Sstr obtained by the coding of the shape value Spel when the block transparency information Dtran indicates that the target block is not an outside-object block. Further, the pixel encoder 5 has a structure which does not perform the coding of the pixel value Vpel when the block transparency information Dtran indicates that the target block is an outside-object block, and outputs pixel coded data Vstr obtained by the coding of the pixel value Vpel when the block transparency information Dtran indicates that the target block is not an outside-object block.
Further, the image coding apparatus 200 has a multiplexer 6 for multiplexing the shape coded data Sstr and the pixel coded data Vstr and outputting a multiplex coded signal Vstr.
Next, the operation of the image coding apparatus 200 will be described.
In the image coding apparatus 200, when an image signal having no shape information is successively input for each frame, the IP decision unit 1 decides whether the target VOP to be coded is assumed to be a VOP subjected to intra-frame coding. (I-VOP) or an VOP subjected to inter-frame coded (P-VOP), and outputs a coding mode signal IPmode indicating which one of the intra-coding and inter-coding is performed to the target VOP.
At this time, in the shape extractor 2, the shape value Spel of the object (VOP) in each frame is extracted on the basis of the pixel value Vpel of each frame successively input. Then, in the block transparency judgement unit 3, the judgement as to whether each of the blocks constituting the target VOP is an outside-object block or not is made on the basis of the shape value Spel, and then the block transparency information Dtran indicating the result of the judgement is output block by block. In MPEG4, the coding is performed in block units and macroblock units as in MPEG1 or MPEG2.
In the shape encoder 4, the coding of the shape value Spel of the target VOP is performed block by block on the basis of the block transparency information Dtran and the coding mode signal IPmode. To be specific, when the block transparency information Dtran indicates that the target block in the target VOP is an outside-object block, a code indicating that the target block is an outside-object block is output. When the block transparency information Dtran indicates that the target block in the target VOP is not an outside-object block, a shape coded data Sstr which is obtained by coding the shape value Spel of the target block are output. At this time, as the coding of the shape value Spel of the target block, one of the intra-frame coding and inter-frame coding is performed in accordance with the coding mode signal IPmode.
In the pixel encoder 5, the coding of the pixel value Vpel of the target VOP is performed block by block on the basis of the shape value Spel, the block transparency information Dtran, and the coding mode signal IPmode. To be specific, when the block transparency information Dtran indicates that the target block in the target VOP is an outside-object block, the coding for the target block is not performed, and when the block transparency information Dtran indicates that the target block in the target VOP is not an outside-object block, the pixel coded data Vstr which is obtained by coding the pixel value Vpel of the target block are output. At this time, as the coding for the pixel value Vpel of the target block, one of the intra-frame coding and inter-frame coding is performed in accordance with the coding mode signal IPmode.
Then, in the multiplexer 6, the shape coded data Sstr and the pixel coded data Vstr are multiplexed and a multiplex coded signal VSstr is output.
When inside-object pixels and outside-pixels are mixed in the target block (unit of coding), in the pixel encoder 5, the target block is subjected to a padding process according to MPEG4 with reference to the shape value Spel, for replacing pixel values of outside-object pixels with pixel values of inside-object pixels, and the coding process is carried out for the pixel values Vpel which have been subjected to the padding process. When this padding process is performed, compression efficiency and image quality improvement of the pixel values can be realized.
FIGS. 26(a) to 26(c) are diagrams for explaining a data structure of a coded signal which is compliant with MPEG4. FIG. 26(a) shows a data structure of an image coded signal having no shape information. As described above, xe2x80x9cVOPxe2x80x9d is a term for representing a screen in MPEG4 and corresponds to the concept of xe2x80x9cframexe2x80x9d.
The coded signal (pixel value signal) Vstr having no shape information is composed of VOP headers Vvoph and pixel-related data Vmb corresponding to each macroblock, like the image coded signal defined in MPEG1 or MPEG2.
The data Vmb of each macroblock is composed of a coding mode signal Vmode and a coded data of a pixel value (pixel value code) Vcode. The coding mode signal Vmode includes coding type information Vtype and a motion vector Vmv. Here, the coding mode signal Vmode includes information for distinguishing between an intra block subjected to the intra-frame coding and an inter block subjected to the inter-frame coding, information for distinguishing between the presence and absence of motion vector data, and information for distinguishing between the presence and absence of pixel data.
In some cases, the coding of the motion vector or pixel value is omitted in accordance with each distinguishing information in the coding mode signal.
FIG. 26(b) shows a data structure of a coded signal having only shape information (shape signal). Here, the coded signal having only the shape information (shape signal) Sstr means that it includes no pixel information.
The coded signal Sstr including only the shape information is composed of VOP headers Svoph and shape-related data Smb corresponding to each macroblock, like the above-mentioned coded signal Vstr having no shape information.
The data Smb of each macroblock is composed of a coding mode signal Smode and coded data of a shape value (shape value code) Scode. The coding mode signal Smode includes a coding type information Stype and a motion vector Smv. The coding mode signal Smode includes information for distinguishing between an intra block subjected to the intra-frame coding and an inter block subjected to the inter-frame coding, information for distinguishing between the presence or absence of motion vector data, and information for distinguishing between the presence or absence of shape data.
FIG. 26(c) shows a data structure of a coded signal (pixel value signal) VSstr having shape information and pixel information. In this coded signal VSstr, the shape-related data Smb and pixel-related data Vmb are alternately arranged subsequent to VOP headers VSvoph, for each macroblock.
The coding of the pixel-related data is omitted for a target macroblock which has been judged to be an outside-object macroblock on the basis of the shape-related data.
However, it is not easy to extract shape information of an object (an image of a specific area) included in a natural image, from an image signal obtained by taking a picture of the natural image by a camera.
Practically, as a method for extracting the shape information, there is almost only a method for taking an image in an equipped environment such as a studio, subjecting an image signal which is obtained by this image-taking to the chromakey processing, and extracting the shape of the specific area in the image. In this shape information extraction method, it is difficult to realize a coding apparatus which makes the most of the features of MPEG4 principally executing the coding in object units.
It is an object of the present invention to provide an image coding method for making the most of the features of MPEG4 principally executing the coding in object units, i.e., separates a desired object (an image of a specific area) in a natural image from another region, and performing the coding for an image signal having no shape information, which is obtained by taking a picture of the natural image, and an image coding apparatus utilizing this image coding method, and a data storage medium which contains a program for realizing the image coding method by software.
Other objects and advantages of the present invention will become apparent from the detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit and scope of the invention will be apparent to those of skill in the art from the detailed description.
An image coding method according to a 1st aspect of the present invention, for coding pixel information which is included in an image signal of an image to be reproduced and forms a design of the image on a pixel frame, on the basis of shape information indicating an arbitrary shape on a shape frame, comprises: a pixel coding process for coding pixel information which forms a design of an area in the image, corresponding to a prescribed shape on the basis of predetermined shape information used as the shape information, which has been previously generated independently of the pixel information included in the image signal and indicates the prescribed shape on a predetermined shape frame; and a multiplexing process for generating coded data which include pixel coded data obtained by the coding of the pixel information and shape coded data corresponding to the predetermined shape information. Therefore, the coding process for the image signal having no shape information obtained by taking a picture of a natural image or the like can be performed, with making the most of the features of MPEG4 principally executing the coding process in object units, i.e., by separating a desired object (an image of a specific area) in the natural image from another area.
According to a 2nd aspect of the present invention, in the image coding method of the 1st aspect, the pixel coding process is carried out such that, on the basis of decoded shape information used as the shape information, which is obtained by decoding the shape coded data corresponding to the predetermined shape information which has been previously generated independently of the pixel information included in the image signal and indicates the prescribed shape on the predetermined shape frame, pixel information which forms a design of an area in the image corresponding to the decoded shape information is coded. Therefore, the coding process for the image signal having no shape information obtained by taking a picture of a natural image or the like can be performed, with making the most of the features of MPEG4 principally executing the coding process in object units, i.e., by separating a desired object (an image of a specific area) in the natural image from other area.
According to a 3rd aspect of the present invention, in the image coding method of the 1st aspect, a shape coding process is carried out for coding predetermined shape information used as the shape information, which has been previously generated independently of the pixel information included in the image signal and indicates the prescribed shape on the predetermined shape frame; and the multiplexing process is carried out such that coded data which include shape coded data obtained by the coding of the predetermined shape information and the pixel coded data obtained by the coding of the pixel information are generated. Therefore, the coding process for the image signal having no shape information obtained by taking a picture of a natural image or the like can be performed, with making the most of the features of MPEG4 principally executing the coding process in object units, i.e., by separating a desired object (an image of a specific area) in the natural image from another area.
According to a 4th aspect of the present invention, in the image coding method of the 1st aspect, decoded shape information which is obtained by decoding the shape coded data corresponding to the predetermined shape information which has been previously generated independently of the pixel information included in the image signal and indicates the prescribed shape on the predetermined shape frame is used as the shape information, a shape coding process is carried out for coding the predetermined decoded shape information, the pixel coding process is carried out such that pixel information which forms a design of an area in the image, corresponding to the decoded shape information, is coded on the basis of the predetermined decoded shape information, and the multiplexing process is carried out such that coded data which include shape coded data obtained by coding of the predetermined decoded shape information and the pixel coded data obtained by the coding of the pixel information are generated. Therefore, the coding process for the image signal having no shape information obtained by taking a picture of a natural image or the like can be performed, with making the most of the features of MPEG4 principally executing the coding process in object units, i.e., by separating a desired object (an image of a specific area) in the natural image from another area.
According to a 5th aspect of the present invention, in the image coding method of the 1st aspect, the pixel coding process is carried out such that shape information corresponding to a prescribed number of predetermined shape frames is used as the predetermined shape information, and the prescribed number of the predetermined shape frames are repeatedly allocated to plural pixel frames which are more than the number of the predetermined shape frames, and pixel information corresponding to the plural pixel frames is coded on the basis of the shape information corresponding to the predetermined shape frames. Therefore, the previously prepared predetermined shape information can be used effectively.
According to a 6th aspect of the present invention, in the image coding method of the 1st aspect, the pixel coding process is carried out such that shape information corresponding to a prescribed number of predetermined shape frames is used as the predetermined shape information, and the prescribed number of the predetermined shape frames are repeatedly allocated to plural pixel frames which are more than the number of the predetermined shape frames, in an order of the predetermined shape frames, and pixel information corresponding to the plural pixel frames is coded on the basis of the shape information corresponding to the predetermined shape frames. Therefore, the order of the predetermined shape frames which are made to correspond to the pixel frames becomes the same as the original order of the predetermined shape frames, regardless of the display times of the pixel frames. Accordingly, in place of the shape value, a shape signal obtained by coding the shape value can be utilized as the previously prepared shape information.
According to a 7th aspect of the present invention, in the image coding method of the 1st aspect, the pixel coding process is carried out such that shape information corresponding to a prescribed number of predetermined shape frames is used as the predetermined shape information, and a predetermined shape frame depending on time information which is set for each pixel frame is allocated to each of plural pixel frames which are more than the number of the predetermined shape frames, and pixel information corresponding to the plural pixel frames is coded on the basis of the shape information corresponding to the predetermined shape frames. Therefore, the display times of the predetermined shape frames which are made to correspond to the pixel frames become almost the same as the display times which are originally set for the predetermined shape frames, and the display of each of the shape frames which are made to correspond to the pixel frames is carried out at approximately original display timing. Consequently, the changes in the shape of a displayed image are prevented from becoming extremely abrupt or slow.
According to an 8th aspect of the present invention, in the image coding method of the 1st aspect, the predetermined shape information includes shape coded data which are obtained by previously coding shape values forming the predetermined shape frame, for each of given unit areas partitioning the predetermined shape frame, by a method which is suitable for a coding process of the pixel information. Therefore, the capacity of the memory which contains the shape information can be saved, whereby the costs can be reduced.
According to a 9th aspect of the present invention, in the image coding method of the 1st aspect, shape values forming the predetermined shape frame and first shape coded data which are obtained by previously coding the shape values by a method which is suitable for a coding process for the pixel information are used as the predetermined shape information, a shape coding process is carried out for coding the shape values forming the predetermined shape frame, as needed, by a method according to a method of a coding process for a pixel frame corresponding to the predetermined shape frame to generate second shape coded data, and the multiplexing process is carried out such that a suitable stream part in the first shape coded data, the stream part corresponding to a predetermined shape frame which conforms to a method for coding a pixel frame, and the pixel coded data are multiplexed, and an unsuitable stream part in the first shape coded data, the stream part corresponding to a predetermined shape frame which does not conform to the coding method of the pixel frame is replaced with a corresponding stream part in the second shape coded data, and the corresponding stream part and the pixel coded data are multiplexed. Therefore, shape coded data which are obtained by subjecting the shape value to the intra-frame coding are employed when the target pixel frame is an intra-frame coded frame, for example, and in other cases the shape signal included in the input shape information is employed as the shape coded data. Accordingly, this image coding method can handle cases where the input shape coded data are obtained by subjecting the pixel value to the inter-frame coding, all of which correspond to the inter shape frames.
According to a 10th aspect of the present invention, in the image coding method of the 9th aspect, the first shape coded data are obtained by subjecting all of the shape values forming the predetermined shape frame to intra-frame coding. Therefore, whether the pixel frame is a frame subjected to intra-frame coding or a frame subjected to inter-frame coding, shape coded data can be used as information of a shape frame corresponding to the pixel frame.
According to an 11th aspect of the present invention, in the image coding method of the 8th aspect, the predetermined shape information includes: in addition to the shape coded data, partition data for distinguishing partitions of stream parts corresponding to areas as units of coding, which partition each predetermined shape frame in the shape coded data; and a decoded shape value which is obtained by decoding the shape coded data. Therefore, the capacity of the memory which contains input shape information can be saved.
According to a 12th aspect of the present invention, in the image coding method of the 8th aspect, the predetermined shape information includes: in addition to the shape coded data, partition data for distinguishing partitions of stream parts corresponding to areas as units of coding, which partition each predetermined shape frame in the shape coded data; data for distinguishing whether a coding process for a pixel value is to be preformed to an area in a pixel frame corresponding to the area as the unit of coding in the predetermined shape frame; and a decoded shape value which is obtained by decoding the shape coded data. Therefore, the capacity of the memory which contains the input shape information can be saved.
According to a 13th aspect of the present invention, in the image coding method of the 1st aspect, when the size of the pixel frame is different from the size of a predetermined shape frame corresponding to the pixel frame, predetermined shape information having no corresponding pixel information is assumed to be information outside a coding target, which corresponds to an outside part of a shape on the predetermined shape frame and to which a coding process is not performed. Therefore, also when the size of the pixel frame is different from the size of the predetermined shape frame, the coding process for the image signal having no shape information can be performed in object units, with using a shape value independent of the image signal.
According to a 14th aspect of the present invention, in the image coding method of the 3rd aspect, the shape coding process is carried out such that, when the size of the pixel frame is different from the size of a predetermined shape frame corresponding to the pixel frame, a shape size conversion process for converting the predetermined shape information so that the size of the predetermined shape frame matches the size of the corresponding pixel frame is carried out, as well as coding of predetermined shape information having the converted size being carried out, the pixel coding process is carried out such that pixel information which forms a design of an area in the image, corresponding to the predetermined shape information having the converted size, is coded on the basis of the predetermined shape information having the converted size, and the multiplexing process is carried out such that coded data which include shape coded data obtained by coding of the predetermined shape information having the converted size and the pixel coded data obtained by the coding of the pixel information are generated. Therefore, when the size of the pixel frame is different from the size of the predetermined shape frame, a process for matching the size of the predetermined shape frame with the size of the pixel frame can be performed easily without processing the pixel information.
According to a 15th aspect of the present invention, in the image coding method of the 4th aspect, the shape coding process is carried out such that, when the size of the pixel frame is different from the size of a predetermined shape frame corresponding to the pixel frame, a shape size conversion process for converting the predetermined shape information so that the size of the predetermined shape frame matches the size of the corresponding pixel frame is carried out, as well as coding of predetermined shape information having the converted size being carried out, the pixel coding process is carried out such that pixel information which forms a design of an area in the image, corresponding to the predetermined shape information having the converted size, is coded on the basis of the predetermined shape information having the converted size, and the multiplexing process is carried out such that coded data which include shape coded data obtained by coding of the predetermined shape information having the converted size and the pixel coded data obtained by the coding of the pixel information are generated. Therefore, when the size of the pixel frame is different from the size of the predetermined shape frame, a process for matching the size of the predetermined shape frame with the size of the pixel frame can be performed easily without processing the pixel information.
According to a 16th aspect of the present invention, in the image coding method of the 1st aspect, the pixel coding process is carried out such that, when the size of the pixel frame is different from the size of a predetermined shape frame corresponding to the pixel frame, a pixel size conversion process for converting pixel information corresponding to the pixel frame so that the size of the pixel frame matches the size of the corresponding predetermined shape frame is carried out, as well as coding of the pixel information having the converted size in the image, which forms the design of the area corresponding to the prescribed shape, being carried out on the basis of the predetermined shape information, and the multiplexing process is carried out such that coded data which include pixel coded data obtained by coding the pixel information having the converted size and shape coded data corresponding to the predetermined shape information are generated. Therefore, when the size of the pixel frame is different from the size of the predetermined shape frame, a process for matching the size of the pixel frame with the size of the predetermined shape frame can be performed easily without processing the shape information.
An image coding apparatus according to a 17th aspect of the present invention, for coding pixel information which is included in an image signal of an image to be reproduced and forms a design of the image on a pixel frame, on the basis of shape information indicating an arbitrary shape on a shape frame, comprises: a pixel encoder for coding pixel information which forms a design of an area in the image, corresponding to a prescribed shape on the basis of predetermined shape information used as the shape information, which has been previously generated independently of the pixel information included in the image signal and indicates the prescribed shape on a predetermined shape frame, and outputting pixel coded data; and a multiplexer for generating coded data which include the pixel coded data and shape coded data corresponding to the predetermined shape information. Therefore, the coding process for the image signal having no shape information obtained by taking a picture of a natural image or the like can be performed, with making the most of the features of MPEG4 principally executing the coding process in object units, i.e., by separating a desired object (an image of a specific area) in the natural image from another area. Further, the quantity of the operation of the shape encoder can be reduced and the high-speed image coding apparatus can be realized.
According to an 18th aspect of the present invention, there is provided a data storage medium which contains a program for implementing an image coding process for coding pixel information which is included in an image signal of an image to be reproduced and forms a design of the image on a pixel frame, on the basis of shape information indicating an arbitrary shape on a shape frame, by a computer, this program is an image coding program for performing, by the computer: a pixel coding process for coding pixel information which forms a design of an area in the image, corresponding to a prescribed shape on the basis of predetermined shape information previously generated independently of pixel information used as the shape information, which is included in the image signal and indicates the prescribed shape; and a multiplexing process for generating coded data which include pixel coded data obtained by the coding of the pixel information and shape coded data corresponding to the prescribed shape information. Therefore, the coding process for the image signal having no shape information obtained by taking a picture of a natural image or the like can be performed by the computer, with making the most of the features of MPEG4 principally executing the coding in object units.